1. Field of the Invention
This invention relates to apparatus having correlated emitter-detector pairs for determining the amount of electromagnetic radiation received at a detector from its paired emitter. It relates particularly, though not exclusively, to optical (including infra-red) touch screen display screens, which may be integrated as part of an Organic Light Emitting Diode (OLED) display device.
2. Related Technology
It is known to provide infra-red touch screen technology integrated into Liquid Crystal Diode (LCD) displays. However, such technology can only detect the presence of an object touching the screen; it does not actually provide images of the objects, hence does not provide information regarding their size and shape and cannot, for example, recognize bar codes. Furthermore, it has proved difficult to integrate infra-red emitters and detectors onto a single back plane together with the LCDs. In general, the infra-red emitters and detectors are positioned behind the LCD plane, which is more complicated, and therefore costly, to manufacture.
Near field optical touch screens are known, in which the presence of a near field object, i.e. an object that is close to, but not actually touching, the display screen is detected using proximity detection. Optical touch screens which detect the presence of an object that actually touches the display screen are also known, where the touching object is detected using Frustrated Total Internal Reflection (FTIR). In this case, the light from the emitter is totally internally reflected from the surface of the display and is detected by detectors positioned in a line from that emitter. If an object touches the surface of the display, the total internal reflection is frustrated, since the light is absorbed by the object touching the surface of the screen. In this way, by having a plurality of rows and columns of detectors, the position of the object can be determined by detecting in which row and which column the total internal reflection is frustrated.
Known touch screen displays having light emitting and light detecting means are described in US 2004/0245438 and US 2006/0244693.